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How the Authy Two-Factor backups work
- taway2012 13y agoGood write-up. Couple of (unsolicited?) review comments. Nitpick: I might be mistaken here, but I think PBKDF2 uses a HMAC function not a simple hash function. So it's highly likely you meant HMAC-SHA256, not SHA-256. Nitpick: I'm guessing the IV is also generated from a cryptographically secure RNG, but you didn't say so in the doc. Question: Why same IV for all user keys, instead of a different IV per key? Best practice is for each "encrypted message" to have a different IV. Your doc makes it look like each user key is a encrypted and sent separately, so each of the user's keys would be a different encrypted message. If my understanding is wrong on anything, would appreciate it if I were corrected. Thx. PS: Opening paragraphs are a bit combative, esp. "So saying ...".